Engines may operate using a plurality of different substances, which may be separately delivered, or delivered in varying ratios, depending on operating conditions. For example, an engine may use a first fuel (ethanol) and a second fuel (gasoline), each with different knock suppression abilities, to reduce engine knock limitations while improving overall fuel economy. As another example, an engine may use fuel injection and water injection.
Various approaches may be used to store different substances on-board a vehicle. For example, the different substances may be stored separately in different storage tanks, and thus filled separately. Alternatively, different substances may be stored in a mixed state, and then separated on-board the vehicle to enable individual control of delivery to the engine.
One approach which allows ethanol to be separated from a blended fuel mixture is described in US 2007/0221163. In US 2007/0221163 a separating device, fluidly coupled downstream of the fuel tank, is used to separate ethanol from a blended fuel mixture. A series of injectors are used to supply the separated fuel to a combustion chamber in the engine. Water may be provided to the separating device to aid in the separation of the ethanol from the blended fuel mixture. The water is recovered from the engine exhaust.
The inventor has recognized several disadvantages with this approach. For example, depending on the conditions and the amount of water in the mixture, the mixture may be subject to freezing. Freezing may in turn degrade separation, as well as various components of the system.
As such, in one approach, a fuel delivery system for an internal combustion engine including a fuel tank, a membrane dividing the fuel tank into at least a first and second portion, the membrane preferentially diffusing a substance from a mixture, the substance having an increased knock suppression relative to the mixture, and a controller adjusting delivery of condensed water to the tank responsive to an operating condition.
In this way, not only is it possible to adjust the rate of separation of a knock suppressing substance via control of condensed water delivery, but in addition it is possible to reduce risks of freezing. As one example, the delivery of condensed water can be reduced under conditions where ambient temperatures are decreased, even when increased water is needed to aid separation.